Vapor-phase corrosion inhibitor



Patented Feb. 24, 1953 VAPOR-PHASE CORROSION INHIBITOR Aaron Wachter, Oakland, and Nathan Stillman, Berkeley, Calif., assignors to Shell Development Company, San Francisco, Calif., a corporation of Delaware No Drawing. Application October 31, 1949, Serial No. 124,727

20 Claims.

This invention relates to corrosion inhibition. More specifically, this invention relates to novel vapor-phase inhibitors, particularly compositions containing such inhibitors, and techniques of utilization thereof.

A vapor-phase corroson inhibitor is a material, preferably solid at room temperature, the gaseous form of which will inhibit corrosion, particularly oxidative corrosion, of metals, especially these metals normally corroded or oxidized by the presence of water vapor in air.

The problems involved in atmospheric corrosion of metals, especially ferruginous metals, by atmospheres containing water vapor and oxygen, e. g., moist or humid air, are well known to manufacturers, handlers, and users of such metals. Prior to the discovery of vapor-phase corrosion inhibitors, the only methods for combating such corrosion were either to separate the metals from the corrosive atmosphere with a coating, such as a paint, oil, or grease, or to extract one or more of the corrosive elements from the atmosphere, such as by the use of a dehydrating agent to dry the air. These methods are, in general, either too time-consuming or too ineffective to be completely satisfactory. However, under proper circumstances, as described more fully below, the use of vapor-phase corrosion inhibitors provides a simple and very satisfactory solution to the problems of corrosion.

It is, therefore, an object of this invention to provide novel and effective vapor-phase corrosion inhibitors and compositions. It is another object of the present invention to provide new methods utilizing, and combinations including, such inhibitors and compositions. Additional objects will be obvious from the description hereinafter.

It has now been found that certain amine salts of carboxylic acids are efiective vapor-phase corrosion inhibitors. Particularly efiective are those salts formed by the interaction of a nonaromatic amine and a weak carboxylic organic acid. Preferred compounds for use in accordance with this invention are the salts of non-aromatic amines having not more than 25 carbon atoms per molecule and carboxylic acids having a dissociation constant between about and 10- The organic bases, salts of which are suitable for use according to this invention, are for example, those disclosed in the copending applications Serial No. 663,608, filed April 19, 1946, Serial No. 668,015, filed May 7, 1946, Serial No. 706,098, filed October 28, 1946, Serial No. 668,016, filed 'May 7, 1946, now abandoned, Serial No. 681,768,

now Patent No. 2,577,219, filed July 6, 1946, and Serial No. 673,886, filed June 1, 1946, of which applications the present application is a continuation-in-part, and which applications were in turn continuations-in-part of application Serial No. 557,358, filed October 5, 1944, now abandoned, which latter application was a continuation-in-part of application Serial No. 492,640, filed June 28, 1943, now issued as United States Patent No. 2,419,327, dated April 22, 1947, and in the application Serial No. 782,047, filed October 24, 1947, of which application the present application is also a continuation-in-part. The only limitation which need be placed upon the nonaromatic amines which are useful for forming vapor-phase corrosion inhibitor salts is one pertaining to the size of the molecule. For some reason not altogether clear, salts formed from bases having too high a molecular weight are not effective inhibitors. Consequently, the bases should contain not more than about 35 carbon atoms, and preferably not more than about 20 or 26 carbon atoms.

Although the salts formed from the above amines with any carboxylic acids are effective vapor-phase corrosion inhibitors, better results are obtained with the organic base salts of the weak acids, particularly organic carboxylic acids having a dissociation constant between about 10- and about 10*, and preferably between about 10- and 10 Thus, the carboxylic acids all are capable of producing efiective vapor-phase corrosion inhibitors as salts of organic bases.

As stated hereinbefore, the salts of this invention are the amine (ammonium) salts, of carboxylic acids, such as, the fatty acids, e. g., lauric, palmitic, stearic, n-butyric, etc.; unsaturated acids such as oleic, maleic, and the like; dibasic acids such as carbonic, phthalic, oxalic, malonic, succinic, glutaric, adipic, pimelic, etc.; aromatic acids such as benzoic, salicylic, and the like.

The metals which are protected by the inhibitors of this invention are those metals which are normally corroded by the water vapor in air. Included in such metals are the ferrous metals such as Armco iron, plain carbon steels of high, low and medium carbon content and cast irons, ferruginous alloys, including high alloy content steels, ferritic and austenitic steels, and the like. Also protected by the inhibitors of this invention are various non-ferrous metals such as copper, aluminum, magnesium, etc., and the non-ferrous alloys of such. Thus, in general, those metals, the oxides of which are spontaneously formed under ordinary temperature and pressure conditions, are protected according to this invention. Protection also has been achieved for couples of dissimilar metals, such as couples of steel with copper, aluminum, nickel and chromium, and alloys of these metals.

Various techniques are effective in the utilization of :the present salts as vapor-phase corrosion inhibitors. Within any enclosing means or container, corrosion of metal surfaces by moisture is prevented by the presence, in the enclosed gaseous atmosphere, of very small amounts of the above compounds. These compounds may be orginally introduced into the enclosure as a-solid, liquid, or vapor, in a solution, .or as an emulsion or a dispersion, etc., just so long as the inhibitor vapors may diffuse throughout the atmosphere in contact with the metal within the enclosure. Thus, a metal article may be placed in a container together with the inhibitors as crystals or as a powder; or there may be introduced into theenclosure-tor:container :a solid material, pref erabl-y an absorbent .or fibrous material, coated or impregnated with the present salts.

In apreferred embodiment of the instant .in- .vention, the present vapor-phase inhibitors are .coated upon, or impregnated within, a solid sheet packaging or wrapping material, such as paper, cardboard, cloth -.or various textile materials, metal foil, plastic films orsheets, and the like, which may be used for packaging metallic objects. Laminates of the above materials, only parts of which are impregnated with, or otherwise contain, the above inhibitors, are also useful. In the case of the latter type of packaging .ma-

terial, the metal is preferably wrapped so that theinhibitor-containing side of the wrapping is toward the metal. Thesalts may be impregnated inthe-wrappingsby various means, such .as, .e. g., dissolving .them (the inhibitors) in .a relatively volatile solvent therefor, such as acetone, alcoho l, or :water soaking the wrapping in the resultingsolutionand allowing the solvent to evaporate. Or the salts may be impregnated in the carrier by successive treatments with solutions of reactants for forming the salts within the carrier. various-materials,..such asby means of a suspension in an adhesive starchor the like.

.Afterp-roviding the containers with the inhibitors inany of the .above .or equivalent forms, the

containers may then be'closed or sealed. The re- .sultant container or package need not be completely airtight, but only has to be closed to the extent that a corrosion-inhibiting concentration of vapors isretained .or maintained within the package.

Incases wherein free circulation :of air is prevented around metal articles in storage, the inhibitors are also efiec'tively utilized by introducing them as vapors around the metal articles. Corrosion by circulation of air 'over metal surfaces can be prevented by partially or substantially saturating the introduced air with vapors of'the inhibitors. Metal parts can be effectively corrosion-proofed by coating them with the in- 'h'ibitors by depositing the latter from a solution or a dispersion, or from heated vapors contacting a cooler metal, or by incorporating the in- "hibitors .in relatively non-volatile coating .ma-

by otherwise making the inhibitors available,

Within vapor spaces "therein.

The .inhibitorsmay also be coated on the Aerosols are also effective for distributing the inhibitors. In such a case, the inhibitor is dissolved in a liquefied normally-gaseous solvent which is under suflicient pressure in a vessel to maintain the solvent in a liquid state. The solution .of the inhibitor thus prepared is released through a restricted orifice in the vessel, thereby distributing the inhibitor in a state of minute subdivision.

A particularly advantageous characteristic of the vapor-phase corrosion inhibitors stems from the facts that .the inhibitors are efiective in extremely low concentrations in the vapor phase and that, under ordinary atmospheric conditions of temperature and pressure, they are relatively stable solids having very low volatilities. Thus,

the condensed inhibitor acts as a reservoir to replace inhibitor vapors which escape from the enclosure are used up, or are otherwise removed from the corrosion-inhibiting atmosphere.

From the above, it is obvious that the duration, but not the degree, .of corrosion protection is dependent upon the amounts of solid'salts'used in accordance with this invention, with the ob vious reservation that the initial supply must be sufficient to build up a corrosion-inhibiting con centration, but minute amounts of inhibitor will usually satisfy this latter requirement. Consequently, the amount to be used in any particular application .will depend upon such things as the length of time for which protection is required and upon the rate at which the inhibitor is allowed to escape, and will vary with the individual applications. In general, satisfactory results are attained when the inhibitor is present in an amount of'between about 0.01 gm. and about '15 gm. (for average conditions, about 1 to 4 gm), per cubic foot of enclosed vapor space. In the case of Wrapping, or packaging materials, 'between about 0.01 gm. and about 5 gm. of inhibitor per square foot of sheet material is generally satisfactory. It should be obvious, however, that extreme conditions may require much greater or much smaller amounts than those stated.

Even though the present inhibitors will give very effective corrosion inhibition when used in dividually, it may often be advantageous "to use a combination of two or more inhibitors. For example, under conditions such as might be-encountered in arctic climates, it has been found that a mixture of 3 parts of anamine'n'itritesalt Example Clean air at a controlled rate of 1201-20 cc. (S. T. P.) per minute was bubbled through 1% sodium chloride solution and then successively passed through 4 glass tubes, each .6 inches long and 31 mm. inside diameter. The first two tubes served as spray traps for entrained water. 'The third tube was lined with paper impregnated with a vapor-phase corrosion inhibitor at a concentrat on of 1 grampersquare foot of paper. The fourth tube contained a polished specimen of SAE .1045 steel mounted in Bakelite so that only one plane surface was exposed to the moist air stream. The equipment was maintained in an oven at 150 F.:t5 F., and the air was approximately the same temperature. Results obtained after a 24-hour test were as follows:

Percent of Specimen Vapor-Phase Corrosion-Inhibitor Surface Covered with Rust Control 1 (unimpregnated paper) 15 cyclohexylammonium benzoate his (cyclohexylammonium) phtha1ate 5 cyclohexylammoniurn laurate 0 cyclohe'xylammonium oleate 1 3,3,5-trimethylcylohexylammonium benzoat Trace cyclohexylammonium p-tertiary butyl benzoate O cyclohexylammonium phenylacetate l 1 Average of seven control samples; one

run with each of the tabuated inhibitors.

The invention claimed is:

1. A corrosion-inhibiting wrapping material comprising paper having hysically incorporated therewith an effective vapor phase corrosion inhibiting amount of cyclohexylammonium laurate.

2. A substantially solid inactive material having physically incorporated therewith an effective vapor phase corrosion inhibiting amount of cyclohexylammonium laurate.

3. The combination comprising a metal article normally corrodible by contact with water vapor and air, an effective vapor phase corrosion inhibiting amount of solid cyclohexylammonium laurate, and an enclosing container for the metal article and. the solid cyclohexylammonium laurate, said metal article and said solid cyclohexylammonium laurate being in positions relative to each other such that the surface of said metal article is contacted by a corrosion inhibiting concentration of the vapors of said solid cyclohexylammonium laurate.

4. A method for inhibiting corrosion of a metal surface normally corrodible by contact with water vapor and air, which includes the step of placing said metal surface and solid cyclohexylammonium laurate in locations relative to each other such that the metal surface is contacted by a corrosion inhibiting concentration of the vapors of said solid cyclohexylammonium laurate.

5. A substantially solid inactive material having physically incorporated therewith an effective vapor phase corrosion-inhibitin amount of a non-aromatic amine salt of a carboxylic acid, the amine portion of said salt having not greater than about 35 carbon atoms therein.

6. The material of claim 5 in which the amine portion of the salt has not greater than about 25 carbon atoms therein, and in which the carboxylic acid has a dissociation constant between about and 10- 7. The material of claim 6 in which the substantially solid inactive material is paper.

8. The material of claim 7 in which the nonaromatic amine is an aliphatic amine.

9. The material of claim 7 in which the nonaromatic amine is a cycloaliphatic amine.

10. The material of claim 7 in which the nonaromatic amine is cyclohexylamine.

11. The material of claim 9 in which the carboxylic acid is phthalic acid.

12. The material of claim 9 in which the carboxylic acid is oleic acid.

13. The material of claim 9 in which the carboxylic acid is benzoic acid.

14. The material of claim 9 in which the carboxylic acid is lauric acid.

15. A method for inhibiting corrosion of a metal surface normally corrodible by contact with water vapor and air, which includes the step of placing said metal surface and a solid salt of a carboxylic acid and of a non-aromatic amine, said amine having not greater than about 35 carbon atoms therein, in locations relative to each other such that the metal surface is contacted by a corrosion-inhibiting concentration of th? vapors of said solid salt.

16. The method of claim 15 in which the carboxylic acid has a dissociation constant between about 10- and 10- and in which the non-aromatic amine has not greater than about 25 carbon atoms therein.

17. The method of claim 16 in which the nonaromatic amine is a cycloaliphatic amine.

18. The combination comprising a metal article normally corrodibl by contact with water vapor and air, a solid salt of a carboxylic acid and of a non-aromatic amine, said amine having not greater than about 35 carbon atoms therein, and an enclosing container for the metal article and the salt, said metal article and said salt being in positions relative to each other such that the metal surface is contacted by a corrosioninhibiting concentration of the vapors of said solid salt.

19. The combination of claim 18 in which the carboxylic acid has a dissociation constant between about 10- and 10- and in which the non-aromatic amine has not greater than about 25 carbon atoms therein.

20. The combination of claim 19 in which the non-aromatic amine is a cycloaliphatic amine.

AARON WACHTER. NATHAN STILLMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,297,666 Wachter Sept. 29, 1942 2,323,369 Briggmann July 6, 1943 2,344,404 Giloy Mar. 14, 1944 2,475,186 Kamlet July 5, 1949 2,512,949 Lieber June 27, 1950 2,522,430 Camp Sept. 12, 1950 FQREIGN PATENTS Number Country Date 117,177 Sweden Sept. 5, 1945 

